Low-molecular-weight polyelectrolytes, such as, for example, EDTA, triphosphates, but also aminomethylenephosphonic acids, have wide practical applications, due to their good calcium- and heavy-metal-binding capacity. Thus, aminomethylenephosphonic acids are preferably used in the bleaching wash, since they have a larger heavy-metal-binding constant than EDTA. In detergent formulations, the heavy metals present reduce the shelf life of peroxidized compounds, which leads to a reduced bleaching effect. In textile bleaching, the fibers are damaged by the heavy metal cations.
Apart from these low-molecular-weight polyelectrolytes, high-molecular-weight polycarboxylic acids [M. Ragnetti; Tenside, Surfactants, Detergents 26, 30 (1989); W. Leonhardt, R. Peldszus, H. Wegert; Seifen, Ole, Fette, Wachse 113, 511 (1987)], such as polyacrylic acid, polyhydroxyacrylic acid [K. Henning, J. Kandler, H. D. Nielen; Seifen, Ole, Fette, Wachse 103, 571 (1977) and 104, 7 (1978)], polymaleic acid [German Patent No. 2,405,284] or polyglyoxalic acid [U.S. Pat. No. 4,140,676] in phosphate-free or reduced phosphate detergent formulations have become very important. Compared with the low-molecular-weight polyelectrolytes, the high-molecular-weight polycarboxylic acids as so-called co-builders have clearly improved properties. The co-builder effect on the polycarboxylic acids is probably due to a particularly good transport function of water-soluble metal ions, in particular calcium ions, from the aqueous detergent liquor into the water-insoluble zeolites. Thus, the co-builders function as ion exchanger, since on the one hand they bind calcium and on the other hand have to release calcium into the zeolite. This effect has been described by G. Manning [G. S. Manning in "Polyelectrolytes", Ed. E. Selegny, D. Riedel Publ. Comp. Dordrecht 1974 and G. S. Manning, J. Phys. Chem. 88, 6654 (1984)] by means of his theoretical model of ion condensation.
Furthermore, the high-molecular-weight polycarboxylic acids are used, in addition to low-molecular-weight polyelectrolytes, such as aminomethylenephosphonic acids, in the area of scale inhibition of saline water, i.e. the inhibition to precipitation of sparingly soluble salts of earth metals having anti-corrosive alkaline action. The amounts of polyelectrolyte required for scale inhibition are less than stoichiometric and are in the range from 1-100 ppm. It is assumed that for the so-called "threshold effect" the polyelectrolyte is absorbed on the crystallite surface and thus interferes in or completely prevents the crystal growth. Thus, scale inhibition is of great importance not only in the area of detergent formulations but also in crude oil recovery. Without suitable measures for scale inhibition, saline water deposits would rapidly clog the pores to the well and the producing pipe and prevent an effective crude oil recovery. In practice, polyacrylates are preferably used for inhibition of alkaline metal sulfate depositions, while aminomethylenephosphonic acids are preferably used for inhibition of alkaline earth metal carbonate depositions.